The invention relates to an apparatus and method for sealing the cold leg nozzles of a nuclear reactor pressure vessel, and more particularly sealing the cold leg nozzles during maintenance and inspection of associated steam generators and pumps.
In a typical nuclear steam supply system, the nuclear reactor vessel, as well as the steam generators and reactor coolant pumps must be periodically inspected. During the inspection and maintenance of the reactor vessel itself, the closure head is removed from the top of the reactor vessel, and the internals are removed from the interior of the vessel. The vessel and refueling canal are filled with water to act as a radiological shield during servicing. In a once through steam generator of the type manufactured by The Babcock & Wilcox Company, heated water travels through the top of the steam generator during operation and leaves at the bottom thereof. Reactor coolant pumps pump the water back into the reactor through an entrance nozzle, known as a cold leg nozzle which is situated in the same horizontal plane as the outlet nozzle. Thus the introduction of water into the reactor vessel during inspection and maintenance procedures would result in flooding of the lower portion of the steam generators, the reactor coolant pumps, and associated piping leading up to the cold leg nozzles. In the past, various plug arrangements have been suggested for sealing the cold leg piping to permit maintenance and inspection of the reactor coolant pump and lower portions of the steam generator during the inspection period in which the reactor vessel and refueling canal are filled with water. Such arrangements pose the threat of loosening or dislodgement of such a plug and flooding of the associated piping as indicated above.
Means for sealing or plugging pipelines in general are well known in the art, as shown for example by U.S. Pat. No. 4,262,702 (Streich). However, such plugs are not suitable for specialized application required by nuclear reactor maintenance and inspection.
It is therefore an object of the present invention to provide a sealing plug which is reliable in operation, and suitable for nuclear reactor inspection and maintenance procedures.
It is still another object of the invention to provide a plugging means which utilizes the hydrostatic pressure created by the water within the reactor pressure vessel to insure a fail safe plug which will not dislodge in the event of failure of the primary plug sealing means.
It is a further object of the invention to provide a method and apparatus for plugging the cold leg nozzles of a nuclear reactor pressure vessel during maintenance and inspection of same, to permit inspection and maintenance of the reactor coolant pumps, steam generators, and associated piping during the same period of time.